Your best bet is probably Project Gutenberg, which is an awesome site that features mostly public domain works. If you're a more shady type of individual, you can try any of the torrent sites which often have a number of listings.
I downloaded the complete works of James Joyce through Soulseek. I don't often see books come up (except for comics), but then I don't really like ebooks, so I don't look.
I've used DC++ in the past for downloading .pdf books and .cbr comics and whatnot. Most of the users are in Eastern Europe and Scandinavia, but you can usually find a pile of English titles...
